Improvement in bridges



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ALEXANDER Mil-DONALD CAMPBELL, or NEWARK, NEW JERSEY, vAssIeNoR To HrMsELE; CHARLES M. BCLEN, AND FREDERICK K. DAY.

Letters Patent No. 110,546, dated December 27, 1870.

IMPROVEMENT IN BRIDGES.

The Schedule referred to in these L'ettm Patent and making part of the same.

LAALEXANDER MCDoNALD CAMrBELL, of the city .age in compensating-levers, which are actuated by the moving weight upon the roadway; in the means y by which' such weight is made to act upon said levers; in the arrangement of'a series of skew-backs to equalize and distribute the moving weight; in the combination, with the compensating-levers, lof bracing cables extending therefrom over the top'of the towers, aroundthecylinders, and returning to and anchored in the towers; in the employment of cylinders and in the base oi' the towers to overcome the friction on the cables;- and in the combination and arrangement of the several partsmentioned, and the construction of their details, as will hereinafter appear.

In the drawinglignre 1 is a side elevation of my'improved bridge, an(

Figure 2 a plan View of i a portionA of the same, showing the tower and butment walls, and 'a portion g' of the space of the bridge, having the roadway removed to show the lateral bracing.

Figure 3`is an enlarged side view of the central wedge-bearing and compensating-levers.

Figure 4, a side ,view of one of the latter.'

Figure V5, an enlarged fragmentary side View of the roadway and string-piece, and stanchions supporting the latter upon the skew-backswith the hanger-block and lbrace-straps of the latter;

Figure 6enlarged side'and transvisevews of said l1anger-block,.and a portion of the main cable, and one of the friction-pulleys-on which it is supported;

' Figure 7 enlarged end and side views of the trussgirder-and skew-back connection; and

FigureS, side and top view of a portion of the girder-arch. l

The main cables A A are continued from the top of the towers O O around ,drums or. cylinders P1P, whichhaiie their axis firmly secured in the ,heavy mason-'work of the abutments, and thence hack to the "center of the span, where their ends are anchored to the compensating levers H H, at a point above their axis -or pivot F, thereby making the tensile strength of the cable'fully available.

The pivot F is so placed that the long arms of the levers are uppermost, and are suspended by the hangersAGz, G2 from the main cable, .having swivel-joint connections at I I.

A wedge-shaped bea-ring, B, is interposed. between these long arms, on which rest th'e string-pieces L and roadway. The eiect of a moving weight over the roadway at this point, suiicient todepress it vin any degree, acts tothe saine extent on the wedge-piece B,

expanding the longarms of the levers, thereby drawing the two ends ofthe cables A, in opposite directions, (they having lapped each other before fastening,) as indicated by the arrows.

This movementtightens andraises the sag of the cables between the towers, and consequently elevates the crown of the roadway.4 It is in consequence of this movement of the cables that the cylinders l? l? are employed to prevent friction, they .consisting ofi drums of such diameter that-,the largest size of cable required will readily bend around them.

This movement of the cables (which, however, is practically so slight as to be almost imperceptible) is a leading feature of my principle of compensation, the action described being the beginning 'of that which loperates through the entire structure. Thus, the stringers are supported at suitable intervals on transverse truss-girders D' D', which rest on skew-backs (l GO, the feet of which are set in recess of the hangerbloeks G1- G?, which are suspended by the rod Gr, to the main cable.

Those skew-backs which meet in the center have Itheir ends crossed and anchored in the compensating-r levers H H', so that the skew-backs adjust themselves to-theexpansion ofthe levers and tightening ot' the main cable, which raises the crown of thei-oadway at every point, the strain being equally distributed, or nearly so, through all parts of 'the-spamaud no de'- iection can occur from a weight not exceeding the absolute strength of the material to bear.

At intermediate points. between the truss-girders the string-pieces are supportedfrom the skew-backs by stanehions a a, and the hanger-blocks Gr are likewise supportedl by the brace-straps g g, having their ends in each alternate series'ot' skew-backs with turnbuckles i i for tightening, Vand saddles k k'for intermediate support.

Thehanger-blocks have sockets h h., (lig. 6,) on

towers toward each other, is couuteracted by the same force acting in the opposite' di'rection through each cable, as indicated by the arrows.

Friction-drums are provided on the lower caps,A as

shown by dotted lilies at qlq, n'g; 1, for both. the mainand brace-cables, and similar ones in the body of the tower at 1 r, which support and prevent frictionv to the continuation of the cables at these bearings.

Separate cylinders, P P and P' P', are employed for each cable.

The girder-arclles are formed of segments of iron, rolled with a web on one side, the pieces being bolted or riveted with their flat sides together, and joints broken, Vas shown in iig. 8, making a light but strong girder.

Lateral rigidity is obtained bya system ot' bracing shown in fig. 2, in which four radial braces, s s, are connected with a central head, t, and their opposite ends with eyes to the trussgirders D' D', and provided with turn-buckles for tightening.

It will `be noticed that the auxiliarybraces V V balance the tensile strain of cables E E.

This system of construction combines the several advantages of the suspension, truss, and girder principles, and unites them in such a manner'as to insure the utmost stability with lightness, and enables spans of great lengthto bex constructed, the length being limited only by the strength of the materialemployed.

I claim as my inventionl. The' continuation of the main cables A A around sustaining points P P of the abutment, and their anchorage on the bridge, substantially .as set forth.

. 2. In combination with the continuous return-cables A A and E VE, the cylinders -P P and P P', for obviating friction, substantially as set forth.

3. The 'compensating-levers H H, in combination with the return-cables A Aand hangers G1 G, as setV orth.

4. The wedge-bearing B, in combination with the compensating-levers H H, as set forth.l I 5. AIn combination with the levers H H, the skewv'backs Q O C, the adjoining ones connected therewith way, asset forth. l

a'lhecombinatiou of the girder-arches D I) with the compensating-levers H H, asset forth.

7. The friction-pulleys M, in combination with the hangers G and Grz and the cables A A, as set forth.

8., The tower-brace ,cables E Ein combination with the cylinders P' P', Iarranged andanchored, substantially as described. k'

9. The combination of the return-cables A A, compensating-lever`s H H, girders D I), and skewbacks G C C, with or without the tower-brace cables E E, substantially as set forth.

ALEXR. MCDONALD CAMPBELL.,

Witnesses:

KATE N. JONES, O. H. BoLnN.

for equalizing the weight upon all parts of the road# i 

